A prospective study of the roles of certain lymphoid tissues in human carcinogenesis is submitted. Cohorts of patients numbering more than 11,000 who underwent appendectomy, tonsillectomy or adenoidectomy between 1925 and 1936, at the Johns Hopkins Hospital have been assembled. For control purposes, a cohort of demographically similar and cancer-free patients undergoing non-lymphoid surgery for reasons unrelated to cancer has also been identified. It is proposed to trace the various cohorts through time to death or survival as of December 31, 1974. Rates and patterns of cancer mortality will be examined in order to make inferences on the possible roles of the vermiform appendix, palatine tonsils and adenoids at varying ages in the susceptibility of humans to cancer (total and site-specific) as well as in the length of their survival. The significance of this study lies in its possible enhancement of our knowledge of the role of immune factors, including lymphoid organs, in human cancer risk as well as in the implications of positive findings for contemporary surgical practice and cancer prevention.